A browser-based emulator for the Casio FX-870P (also sold as the VX-4) pocket computer has been ported to the web using TypeScript and Vue 3 by Mark Wickens. The original Delphi reference implementation from PISI is now accessible online, emulating the 1986 programmable calculator's Hitachi HD61700 CPU at 921 kHz, 96×64 pixel LCD, 83-key keyboard, serial port, and optional MD-120 floppy drive.

The emulator features a responsive calculator face that scales to any screen, full PC keyboard mapping with shifted-symbol handling, a built-in program library, RS-232C serial emulation with XON/XOFF flow control, and MD-120 disk emulation via Origin Private File System (OPFS). Additional tools include an interactive character set table, a DEFCHR$ pixel editor, turbo mode at ~50x speed, fullscreen mode, firmware toggle between Japanese and English ROMs, a CPU debugger with live registers and disassembly, a BASIC listing panel with syntax highlighting, and a communications panel for UART diagnostics.

The project requires Node.js 22 LTS and ROM files placed in public/roms/. It includes a headless test suite powered by Vitest, a BASIC compiler that generates annotated assembly listings and self-loading programs, and a headless debugger library with breakpoints, memory watchpoints, and instruction tracing. Reference documents cover ROM annotations, full disassembly, user manuals, and implementation notes.